This invention relates to electric rotating machines and more particularly to stepper motors operable with a single-phase or multi-phase current supply.
There has been developed a line of fractional horse power electric motors that are extremely responsive to the incoming signals and highly efficient. Representative motors of this type are disclosed, for example, in Albert Palmero and Charles Hansen U.S. Pat. No. 4,714,853, Arthur W. Haydon and John J. Dean U.S. Pat. Nos. 4,241,270 and 4,274,026, Arthur W. Haydon U.S. Pat. No. 3,671,841, Gotfred O. Hoffmann U.S. Pat. No. 3,671,841 and Roy Copper and Charles Hansen co-pending U.S. Pat. applications Nos. 121,170 and 312,765. The motors customarily are of cylindrical configuration and utilize a nonsalient pole rotor with salient stator poles in magnetic flux relationship with the rotor poles. The stator poles are energized by one or more windings supplied with single phase or multi-phase current and in many cases may be operated as stepper motors in which the rotor moves in discrete rotational increments or steps.
For several applications of such motors it is desirable to maintain a constant rotor velocity and to insure that the rotor is oriented in its proper angular position at all times. Many prior motors have exhibited deficiencies in these respects, and such deficiencies have been of special moment in cases in which the rotors of the motors where subjected to varying loads. As the load increases, for example, the motor tends to lose synchronization with the resulting adverse effect on the motor's velocity and rotor position. To alleviate these difficulties it was often necessary heretofore to over-design the motors and to operate such motors at substantially less than their rated torque capability to provide a safe margin. As a result, the motors were unnecessarily expensive to manufacture and had other disadvantages.